It was big news last week when prosecutors charged George Zimmerman with second-degree murder in the shooting of Trayvon Martin. But Zimmerman could walk free if a judge decides his actions fall under Florida’s “Stand your ground” law, which gives broad leeway to people to shoot in self-defense. There is no way to undo what happened in the Zimmerman-Martin encounter, but some good can still come of it: it could lead states to repeal their misguided “Stand your ground” laws.

Many criminal-law doctrines evolve over centuries, but “Stand your ground” laws arrived suddenly — starting in Florida in 2006. Under traditional legal principles, people in disputes generally have a duty to “de-escalate” in the interest of saving human life, but the Florida law dialed down the historic “duty to retreat.” Now, people would have the same kind of right to stand their ground in public — on the streets, in parking lots and in bars — that they historically had in their homes.

After gaining a foothold in Florida, the “Stand your ground” movement spread quickly to other states. This legal revolution did not just happen. The National Rifle Association (NRA) and its allies lobbied for the changes heavily, arguing that “Stand your ground” is an important gun right. The lobbying effort paid off. Today, 25 states have passed “Stand your ground” laws.

The argument for these laws is that they free people to defend themselves when they reasonably believe they are in danger. The NRA and other supporters argue that state laws that impose a duty to retreat put law-abiding citizens faced with a threat in an unfair position. If they reasonably act to protect themselves, “Stand your ground” supporters say, they will too often be second-guessed by the legal system — and charged with homicide.

But critics have pointed out the obvious problem with “Stand your ground” laws. They encourage people who get caught up in dangerous encounters to up the ante and to shoot when gunfire could have been avoided. The Brady Campaign to Prevent Gun Violence, a pro-gun-control group, has dubbed “Stand your ground” laws “Shoot first” laws. And the National District Attorneys Association (NDAA) has pointed out an oddity of “Stand your ground”: the “blanket immunity” that the Florida law gives to members of the public who fire their guns is actually broader than the leeway the law gives to police, whose job it is to defend public safety.

There is evidence that the critics are right — that these laws do in fact encourage people to turn tense encounters into killings. Five years after Florida’s “Stand your ground” law took effect, the Tampa Bay Timesfound that justifiable homicides in Florida had “spiked”: up from an average of 34 in the first half of the past decade to 105 in 2009. The Washington Post has reported that other states have seen similar jumps. It is not just people who are parties to these encounters who have to worry. As the NDAA has pointed out, needless use of firearms in public places also puts innocent bystanders at risk.

In a Washington, D.C., speech last week, New York City Mayor Michael Bloomberg announced a national campaign to reform or repeal “Stand your ground” laws, which supporters are calling “Second Chance on Shoot First.” The campaign is getting strong support from the NAACP and other civil rights groups, who argue that “Stand your ground” laws are more likely to be used to defend white people who kill blacks than the reverse.

It is odd that many conservatives are rallying around “Stand your ground” laws — because they are actually not conservative at all. Conservatism is the belief that doctrines and practices that have emerged over time are generally there for a good reason and should not be lightly discarded in favor of something better. The old rule of imposing a “duty to retreat” on people before they use deadly force in the street is conservative by this standard — as well as commonsensical.

When people get into disagreements in public places, it is often difficult in the heat of the moment to sort out who is right and who is wrong, and misperceptions are common. Is someone a trespasser or is he just lost? Were they threatening violence, or simply mouthing off? The “Stand your ground” principle encourages people who are in confusing situations of this sort to shoot first and ask questions later. That is an approach that makes it far more likely that these encounters will end up with fatalities.

If Zimmerman does go to trial, there will no doubt be enormous debates over his guilt or innocence. It is difficult to sort out motives and right and wrong in cases of this sort — especially when one of the critical witnesses, young Mr. Martin, cannot testify about what happened. The debate over “Stand your ground” laws, however, should not be as contentious. If these laws are repealed, it will be far more likely that the next time two people like Zimmerman and Martin get into a tense public encounter, both of them will walk away with their lives.